Remove duplicate lines from a large text or given document in java.

import java.io.*;

class FileOperation

{

    public static void main(String[] args) throws IOException

    {

        PrintWriter pw = new PrintWriter("output.txt");

        BufferedReader br1 = new BufferedReader(new FileReader("input.txt"));  

        String line1 = br1.readLine();

        while(line1 != null)

        {

            boolean flag = false;

            BufferedReader br2 = new BufferedReader(new FileReader("output.txt"));

            String line2 = br2.readLine();

            while(line2 != null)

            {

                if(line1.equals(line2))

                {

                    flag = true;

                    break;

                }  

                line2 = br2.readLine();

            }

                if(!flag)

               {

                pw.println(line1);

                pw.flush();

            }

            line1 = br1.readLine();

        }

        br1.close();

        pw.close();

        System.out.println("File operation performed successfully");

    }

}

output:

 

   

THANK YOU!!!!